Since they were obviously make bricks, the grooves may have fit together eliminating the need for mortar.
That would be a logical concept, but have you ever watched a loaf of bread bake? It first swells up and then just before it is done it shrinks a bit. These dimples would have cause it to shrink at different rates therefore kind of “pre-peeling it loose from bottom face surface contact.
So it is pretty much already loose before it is completely done. On a smooth surface it will stick easier because it expands and contracts at the same rate across that surface. An odd surface causes uneven expansion and contraction across the contact face breaking that uniform bond.
The fact that they figured out that reality so far back changes our assumptions about intelligence levels during the Neolithic period. It is pure genius science that we don’t even use now when baking... :)